Stacking skeleton heads



FIG. 1 is a perspective view of the design;

FIG. 2 is a front elevational view of the design;

FIG. 3 is a back elevational view of the design;

FIG. 4 is a left side view of the design;

FIG. 5 is a right side view of the design;

FIG. 6 is a top view of the design; and,

FIG. 7 is a bottom view of the design. 

The ornamental design for stacking skeleton heads, as shown and described. 